算法1

(暴力枚举) $O(n^2)$

BFS

时间复杂度

参考文献

java 代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isCompleteTree(TreeNode root) {
        Queue<TreeNode> q = new LinkedList<>();
        q.offer(root);
        while(!q.isEmpty())
        {
            TreeNode cur=q.poll();
            if(cur==null) 
            {
                //查队列中后面是否有非空个节点
                while(!q.isEmpty())
                {
                    TreeNode temp = q.peek();
                    if(temp!=null) return false;
                    else q.poll();
                }
            }
            else
            {
                q.offer(cur.left);
                q.offer(cur.right);
            }
        }
        return true;
    }
}